Soil and land fact sheet no. 7
Aluminium toxicity
Aluminium is present in many soils but its availability and toxicity to plants depends on soil pH
Aluminium toxicity
occurs in soils which contain aluminium and are strongly acidic. Aluminium availability also increases at high pH, so toxicity is theoretically possible in strongly alkaline soils as well. Aluminium is present in many soils, but its availability to plant roots is pH dependent.Aluminium is typically present in ironstone rich soils and those in which the dominant clay mineral is kaolinite. Sands contain little aluminium, so even strongly acidic sands are rarely toxic. Many plants are sensitive to aluminium even at small concentrations. As a general rule, correction of soil acidity will alleviate aluminium toxicity symptoms.
Land assessment in southern South Australia
Soil extractable aluminium levels (0.01 M calcium chloride) were measured at selected soil characterisation sites, and results were extrapolated over similar environments. Plants vary in their susceptibility to aluminium toxicity, so the three attribute classes used in the assessment of aluminium toxicity (refer to table below) are based on critical levels for aluminium sensitive plants such as lucerne.
Soil properties can vary across the landscape in a subtle or dramatic fashion. Mapping at a regional scale is not able to display this level of variability, however proportions of each Aluminium toxicity class (e.g. TAL1, TAL2, etc.) have been estimated for each map unit.
Further information can be found in Assessing Agricultural Land (Maschmedt 2002).
Two soil profiles from high rainfall zones with strong acidity and high (toxic) levels of aluminium in the rootzone. The soil on the left is an acidic loam over red clay on kaolinized rock from the Fleurieu Peninsula. The soil on the right is a thick bleached sand over mottled brown clay from the South East.
Area statistics
Aluminium toxicity potential Approximate extractable aluminium
(0.01 M CaCl2) Area Cleared land Class*
Low Less than 2 mg/kg 93.88% 93.08% TAL1
Moderate 2–4 mg/kg 4.20% 4.63% TAL2
High More than 4 mg/kg 0.50% 0.60% TAL3
Not applicable 1.42% 1.70% TALX
TOTAL HECTARES 15,765,460 10,439,300
* The letters ‘TAL’ denotes classes that are specific to Aluminium toxicity
Aluminium toxicity Fact sheet
Displaying data in soil maps
Soil and land attribute maps display a simplified version of the underlying data. Mapping classes are based on an interpretation of soil landscape map units, within which aluminium (Al) toxicity can vary significantly. Map units are classified on the proportions of moderate and high toxicity, estimated from limited laboratory analyses and extensive extrapolation according to similarity of soil type. Because aluminium toxicity is highly pH dependent, and pH in turn is highly management dependent, the mapped legend categories are very generalised.
Further information
View data on NatureMaps ( Soils)
Read the metadata for this layer
Read more about soil attribute mapping
Contact Mapland
Download from Enviro Data SA:
Statewide map and spatial dataset
Assessing Agricultural Lands (Maschmedt 2002)
Soils of Southern SA book Part 1 and Part 2
Plant
sensitivity Tolerant species Level above which yield declines*
Very
sensitive Lucerne and canola <2 mg/kg Sensitive Barley, sensitive wheat,
phalaris 2-4 mg/kg
Tolerant
Sub. clover, cocksfoot, perennial rye, tolerant
wheat, phalaris
4-8 mg/kg
Very tolerant Lupins, oats, triticale >8 mg/kg
* Interpretation of soil extractable aluminium levels (0.01 M calcium chloride extractable aluminium)
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© Crown in right of the State of South Australia, through the Department of Environment, Water and Natural Resources 2016. Last updated June 2016.
This work is licensed under the Creative Commons Attribution 4.0 International License.
